Bicycle fork and pivot for same

ABSTRACT

A bicycle includes fork head ( 2 ) from which two sleeves ( 3   a,   3   b ) branch off and, on the side opposite to the sleeves, a tubular pivot ( 4 ) including a lower cylindrical portion ( 4   a ) integral with the fork head, and an upper cylindrical portion ( 4   b ) for fixing a stem. The external diameter (Da) of the lower cylindrical portion ( 4   a ) of the pivot is larger than the external diameter (Db) of the upper cylindrical portion ( 4   b ) of the pivot, and a transitional zone ( 4   c ) links the two parts ( 4   a,   4   b ) with different diameters.

BACKGROUND OF THE INVENTION

The invention relates to a bicycle fork of the kind comprising a forkcrown from where there extend two fork stems and, on the opposite sideto the fork stems, a tubular pivot comprising a cylindrical bottom partsecured to the fork crown, and a cylindrical top part for securing ahandlebar stem.

DESCRIPTION OF THE RELATED ART

It is known that, in a bicycle, the fork pivot is mounted to rotate in abushing of the bicycle frame, generally by means of two rolling bearingsprovided one at the bottom and one at the top of the bushing. Thecyclist, by acting on a handlebar fixed to the end of the handlebarstem, can thus steer the fork, and the front wheel, in a desireddirection.

The connecting region linking the pivot and the fork crown constitutes atrouble spot and is particularly heavily mechanically loaded.

SUMMARY OF THE INVENTION

It is an object of the invention, above all, to provide a bicycle forkwhich, in the connecting region linking the fork crown and the pivot,has satisfactory rigidity and provides the best possible distribution ofstress over the bearings, particularly at the bottom part of the pivot,without this resulting in an appreciable gain in the weight of the forkand of the steering gear.

According to the invention, a bicycle fork of the kind definedpreviously is characterized in that the outside diameter of thecylindrical bottom part of the pivot is greater than the outsidediameter of the cylindrical top part of this pivot, and in that atransition region provides the link between the two, different-diameter,parts of the pivot.

This solution makes it possible to strengthen the connecting regionlinking the fork crown and the pivot, without in any way leading to anappreciable increase in weight because the top part of the pivotmaintains a small outside diameter which involves no appreciablemodification to the weight of the pivot and handlebar stem assembly.

As a preference, the transition region of the pivot has a frustoconicalexterior surface, the outside diameter of which decreases from thebottom part toward the top part.

The fork is advantageously made of composite, preferably as a singlepiece with the pivot which is also made of composite.

The term “composite” is intended to mean a material consisting of fibersof high mechanical strength, particularly carbon or glass fibers,embedded in a resin matrix. Parts manufactured from such a material aregenerally molded.

As an alternative, the pivot may be made of metal, particularly of lightalloy. The fork may also be made of metal.

The pivot may be manufactured separately, then assembled with the forkcrown.

As a preference, the diameter of the top part of the pivot is equal to astandard bicycle pivot diameter, particularly 25.4 mm or 28.6 mm. Thediameter of the bottom part of the pivot is at least 5% (five percent),and advantageously at least 12% twelve percent), greater than thediameter of the top part.

The pivot may have a cylindrical cavity of circular cross section, thediameter of which remains constant from the bottom to the top.

The exterior surface of the connecting region linking the pivot and thefork crown advantageously has a frustoconical surface to act as asupport for a mating surface of an inner ring of a rolling bearing. Inthe case of a fork and of a pivot made of composite, the fibers of thecomposite are continuous in the connecting region.

The invention also relates to a bicycle fork pivot comprising acylindrical bottom part for linking to a fork crown and a cylindricaltop part for the attachment of a handlebar stem, characterized in thatthe outside diameter of the cylindrical bottom part of the pivot isgreater than the outside diameter of the cylindrical top part of thepivot, and in that a transition region provides the link between thetwo, different-diameter, parts.

Advantageously, the transition region of the pivot has a frustoconicalexterior surface, the diameter of which decreases from the bottomupward.

The invention also relates to a bicycle steering gear, particularlyintegrated steering gear, comprising a fork as defined previously.

When the bicycle steering gear comprises a fork with a connecting regionlinking the pivot and the fork crown which has a frustoconical exteriorsurface, the steering gear comprises, at the bottom part of the framebushing, a rolling bearing, the inner ring of which has an obliquebearing surface mating with the frustoconical surface of the linkingregion.

BRIEF DESCRIPTION OF THE DRAWINGS

Apart from the provisions set out hereinabove, the invention consists ina certain number of other provisions which will be dealt with more fullyhereinafter with regard to some exemplary embodiments which aredescribed in detail with reference to the appended drawings but whichare not in any way limiting. In the drawings:

FIG. 1 is a schematic perspective view of a bicycle steering gear.

FIG. 2 is a vertical half section and an external half view of theconnecting region linking the pivot and the fork crown according to theinvention, depicted in part.

FIG. 3 is a vertical section, with partial cutaway, of the pivot and ofthe fork crown and of the bushing of the frame housing the pivot.

FIG. 4 is a perspective view of a vertical section of the fork partiallydepicted and of the pivot.

FIG. 5, finally, is a schematic vertical section of an alternative formof the connecting region linking the pivot and the fork crown.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference to FIG. 1 of the drawings shows a bicycle fork 1 comprising afork crown 2 from which two partially depicted fork stems 3 a, 3 bextend. In the customary way, each fork stem is equipped at its lowerend (not visible) with a lug for attaching the axle of the front wheelwhich passes between the fork stems.

The fork 1 comprises a tubular pivot 4 which, as visible in FIGS. 3 and4, comprises a cylindrical bottom part 4 a of circular cross sectionsecured to the fork crown 2 and a cylindrical upper part 4 b of circularcross section for the attachment of a handlebar stem P. The outsidediameter of the parts 4 a, 4 b is constant.

The expressions “bottom part”, “top part”, “bottom” and “top” must, ofcourse, be understood as applying to a bicycle in the vertical positionfor riding.

The fork 1 is mounted to rotate in a bushing 5 of the bicycle frame C,generally via a first bearing provided at the bottom part between thebushing 5 and the pivot 4 and a second bearing (not depicted) providedat the top part of the bushing 5. In the example illustrated, the firstbearing is formed of a rolling bearing 6, depicted schematically. Ingeneral, the second bearing is also formed of a rolling bearing. The twobearings may, however, be plain bearings.

The connecting region 7 linking the fork crown 2 and the pivot 4constitutes a trouble spot at which the best possible distribution ofstress is desired. The top part 4 b of the pivot, on the other hand, isnot as heavily stressed.

The outside diameter Da of the cylindrical bottom part 4 a of the pivotis greater than the outside diameter Db of the top part 4 b of thepivot. These two different diameters Da, Db are provided on one and thesame piece, namely the pivot 4.

A transition region 4 c provides the link between the two parts 4 a, 4b. This transition region 4 c has a frustoconical exterior surface, thediameter of which decreases from the bottom upward. The region 4 cextends over a relatively long length 1, particularly a length in excessof 5 cm.

At the present time, there are two fork pivot outside diameters asstandard in the field of cycling. A first diameter of 25.4 mm isgenerally used for on-road cycling, while a larger diameter of 28.6 mmis used for mountain bikes, the forks of which are subjected to higherstresses. This larger diameter of 28.6 mm allows for a betterdistribution of stress over the rolling bearings, and an appearance morein tune with frames with oversized tubes.

The diameter Db of the top part may be equal to one of the standardcycling pivot diameters, either 25.4 mm or 28.6 mm at the present time.Of course, the value of the diameter Db is not fixed and may be chosento suit varying requirements, particularly to fit varying standards.

The diameter Da of the bottom part is preferably at least 5%, andadvantageously at least 12%, greater than the diameter Db of the toppart.

The larger diameter Da makes it possible, in the case of a fork made ofcomposite, to cause more fibers to pass from the pivot 4 to the forkcrown 2 in the connecting region 7 situated radially on the inside ofthe rolling bearing or bearing 6. In the case of a metal pivot 4, thelarger diameter Da allows an increase in the moment of inertia and alsoimproves fork behavior.

The pivot 4 has a cylindrical internal cavity 8 of circular internalcross section, the diameter of which remains constant along the entirelength of the pivot. The variation in thickness of the pivot is duesolely to the variation in the outside diameter. Toward the lower end ofthe cylindrical cavity 8, a hole T of axis perpendicular to themid-plane of the fork passes through the fork crown, for the attachmentof a brake caliper.

Two diametral partitions at right angles, forming a cross, may beprovided in the housing 8 to strengthen the pivot, particularly when itis made of composite. The mid-plane of one of the partitions lies alongthe longitudinal plane of symmetry of the fork.

The fork 1 is advantageously designed for integrated steering,illustrated in FIGS. 1 to 3. The steering cups of the lower and upperrolling bearings, invisible, are housed in the larger-diameter ends 5 a,5 b of the bushing 5.

An interior bearing surface 9 (FIG. 2) is machined in the lower end 5 afor supporting the outer ring of the rolling bearing 6. The inner ringof this rolling bearing is supported against an interior bearing surface10 machined on the crown 2 at the base of the pivot 4. There is aminimum clearance 11 between the lower edge of the bushing 5 and thefork crown.

The pivot of the invention makes it possible to maintain the advantagesof the larger diameter at the connection with the fork crown withoutadding excessive weight because it is possible, at the top part, tomount a handlebar stem corresponding to a smaller pivot diameter whichis sufficient for the stresses there are at this point.

The rolling bearing 6 is advantageously manufactured in compact form soas to make it possible, using the same rolling bearing, to produce asteering gear using either a pivot of constant outside diameter foron-road cycling, generally a diameter of 25.4 mm, or a pivot of constantoutside diameter for mountain bikes, generally a diameter of 28.6 mm, orthe pivot according to the invention. For that, the inner ring of therolling bearing has an inside diameter designed for the largest-diameterpivot and an outside diameter compatible with a frame bushing associatedwith a small-diameter pivot, for on-road cycling.

Referring to FIG. 5, it is possible to see a particularly advantageousalternative form of embodiment of the connecting region 107 linking thepivot 104 and the fork crown 102. The various elements have rolessimilar to elements already described previously and are denoted by areference equal to the sum of the previous reference and the number 100.

In FIG. 5, only the bottom part 104 a of the pivot is depicted. Theoutside diameter of the top part (not depicted) of the pivot 104 issmaller than that of this bottom part 104 a.

The rolling bearing 106 comprises an inner ring 106 a, an outer ring 106b, and rolling bodies 106 c, particularly balls, arranged betweenraceways provided in the rings.

The inner ring 106 a has, toward the inside in the radial direction, afrustoconical oblique lower bearing surface 12, the generatrices ofwhich are inclined with respect to the geometric axis of the rollingbearing, advantageously at an angle of 45°. The inner surface in theradial direction of the ring 106 a is extended upward, beyond the smallbase of the frustoconical surface 12, by a cylindrical surface 13, theinside diameter of which has the same value as the outside diameter ofthe part 104 a of the pivot which acts as a guide.

The exterior surface of the part 104 a is extended downward by afrustoconical surface 14, the diameter of which increases downward. Thefrustoconical surface 14 belongs to the exterior surface of theconnecting region 107. The inclination of the generatrices of thesurface 14 to the geometric axis of the fork is the same as that of thegeneratrices of the surface 12 which presses and abuts against thesurface 14.

The outer ring 106 b has an outer surface, in the radial direction,comprising a top part 15 with a frustoconical exterior surface, thediameter of which decreases upward, and a cylindrical bottom part 16 ofthe same diameter as the internal cylindrical surface of the bushing 105of the frame. The inclination of the generatrices of the surface 15 tothe geometric axis of the rolling bearing is advantageously 45°. Ashoulder 17 projecting toward the inside of the bushing 105 is providedwith a frustoconical bearing surface 18 which mates with the surface 15which presses against it.

The connecting region 107 with oblique surface 14 provides a gradualtransition from the bottom part 104 a of the pivot to the fork crown102. In the case of a pivot 104 and a fork crown 102 made of a singlepiece of composite it is possible, by the oblique bearing of thesurfaces 12 and 14 one on the other, to pass numerous continuous fibersF under the rolling bearing 106, from the pivot 104 to the fork crown102. This avoids machining a bearing surface such as 10 in FIG. 2, withthe cutting of fibers.

The continuity of the fibers F is favorable to the mechanical strengthof the connection between the pivot 104 and the fork crown 102.Furthermore, the bearing surface 14 on the fork crown, for the rollingbearing 106, can be obtained directly by molding.

The rolling bearing 106 can be produced in compact form with an insidediameter of the inner ring 106 a as large as possible to allow a greatmany fibers F to be passed through the connecting region 107. The stresslevel is thus reduced in the fragile section, and safety is enhanced.According to an advantageous, but not limiting, exemplary embodiment,the outside diameter of the rolling bearing 106 is equal to 42 mm, andits inside diameter is equal to 33 mm.

When a plain bearing is installed in place of the rolling bearing 6,106, all of the above remains valid.

The fork according to the invention, the pivot of which is combined witha compact rolling bearing 6, 106 or a plain bearing, also offers freedomin the construction of the bicycle. The fork may be chosen independentlyof the bushing 5, 105, making it possible to devise a range by alteringthe diameter of the bushing while at the same time using the samerolling bearing 6, 106. Better mechanical behavior is obtained, andintegrated steering can be used on certain current frames.

What is claimed is:
 1. A bicycle fork, comprising: a fork crown (2); two fork stems (3 a, 3 b) extending from the fork crown; and on a side of the fork crown opposite a side with the two fork stems, a tubular pivot (4, 104), the pivot comprising a cylindrical bottom part (4 a, 104 a) secured to the fork crown, a cylindrical top part (4 b) for securing a handlebar stem without need of a supplemental piece fixed to the fork crown, and a transition region (4 c) linking the top part and the bottom part, an outside diameter (Da) of the cylindrical bottom part (4 a, 104 a) being greater than an outside diameter (Db) of the cylindrical top part (4 b), and the pivot having a frustoconical exterior surface, the outside diameter of the frustoconical exterior surface decreasing from the bottom part upward towards the top part, the fork crown (2), the two fork stems (3 a, 3 b) and, the pivot comprising a single piece made of composite material.
 2. The bicycle fork as claimed in claim 1, characterized in that the diameter (Db) of the top part of the pivot is equal to a standard bicycle pivot diameter.
 3. The bicycle fork as claimed in claim 1, characterized in that the diameter (Da) of the bottom part (4 a, 104 a) of the pivot is at least 5% (five percent) greater than the diameter (Db) of the top part.
 4. The bicycle fork as claimed in claim 3, characterized in that the diameter (Da) of the bottom part (4 a, 104 a) of the pivot is at least 12% (twelve percent) greater than the diameter (Db) of the top part.
 5. The bicycle fork as claimed in claim 1 characterized in that the pivot (4) has a cylindrical cavity (8) of circular cross section, the diameter of which remains constant from the bottom to the top.
 6. The bicycle fork as claimed in claim 1, characterized in that the exterior surface of a connecting region (107) linking the pivot (104) and the fork crown (102) has a frustoconical surface (14) to act as a support for a mating surface of an inner ring of a rolling bearing.
 7. The bicycle fork as claimed in claim 1, characterized in that the exterior surface of a connecting region (107) linking the pivot (104) and the fork crown (102) has a frustoconical surface (14) to act as a support for a mating surface of an inner ring of a rolling bearing and in that fibers (F) of the composite material are continuous in the connecting region (107), from the pivot (104) to the fork crown (102).
 8. A bicycle steering gear, comprising a fork as claimed in claim
 1. 9. A bicycle steering gear, comprising a fork as claimed in claim 6, and, at the bottom part of a frame bushing, a rolling bearing (106), the inner ring (106 a) of which rolling bearing has an oblique bearing surface (12) mating with the frustoconical surface (14) of the linking region (107).
 10. A bicycle steering gear, comprising a fork as claimed in claim 7, and, at the bottom part of the frame bushing, a rolling bearing (106), the inner ring (106 a) of which roller bearing has an oblique bearing surface (12) mating with the frustoconical surface (14) of the linking region (107).
 11. The bicycle fork as claimed in claim 2, characterized in that the diameter (Db) of the top part of the pivot is one of 25.4 mm and 28.6 mm.
 12. A bicycle fork, comprising: a fork crown (2) with two fork stems (3 a, 3 b) extending from a first end of the fork crown and a tubular pivot extending from a second end of the fork crown, opposite the first end, the pivot comprising a cylindrical bottom part (4 a, 104 a), a cylindrical top part (4 b) for securing handlebars, and a transition region (4 c) linking the top part and the bottom part, an outside diameter (Da) of the cylindrical bottom part (4 a, 104 a) being greater than an outside diameter (Db) of the cylindrical top part (4 b), the pivot having a frustoconical exterior surface, the outside diameter of the frustoconical exterior surface progressively decreasing from the bottom part upward towards the top part, wherein, the fork crown (2), the two fork stems (3 a, 3 b) and, the pivot comprise a single piece of composite material.
 13. A bicycle fork, comprising: a single piece, composite material tubular pivot and fork crown, the fork crown merged, at a first end, with two fork stems and, at a second opposite end, with the tubular pivot, the pivot having a reducing wall thickness from a cylindrical bottom part, located at the second end, toward a cylindrical top part, the top part providing a mounting surface for mounting a handlebar stem. 